Method for making lens mold



June 16, 1959 G. w.- ONKSEN ETAL METHOD FOR MAKING LIENS MOLD OriginalFiled March 4 1950 Summers United States Patent 2,890,627 lVIETHOD FORMAKING LENS MOLD George W. Onksen, Anderson, Ind., and Eugene S.Reynolds, Dearborn, Mich., assignors to General Motors Corporation,Detroit, Mich., a corporation of Delaware 2 Claims. (Cl. 9011) Thisapplication is a division of our copending application Serial Number147,724, filed March 4, 1950.

This invention relates generally to the manufacture of lensesfor theheadlamps of tractors and other automotive vehicles, and for othersimilar purposes, and it has particular relation to the manufacture of alens for projecting a particular illumination pattern upon the ground sothat the operation of a tractor or other means for carrying the lamp maybe facilitated.

It is the object of any lens for use in the headlamps of tractors orother automotive vehicles to project the light from the light sourceupon the ground and in front of the vehicle in such a way as'toilluminate the region in front of the vehicle and the ground or road tobe traveled by the vehicle, so that the operation of the vehicle may beobserved and may be made safe and easy for the vehicle operator. It hasbeen the practice heretofore to provide lenses for such headlamps fordiflusing the light thereof according to various desired patterns.

One method of constructing lenses for such purposes is to provideparallel fluted surfaces projecting in different directions uponopposite surfaces of the lens, the purpose of one set of fluted surfacesbeing to diffuse or deflect the light in one direction and of the otherto diffuse the light in a direction normal thereto. In order to providea smooth exterior surface for the lens it has also been proposed tointerpose these parallel and intersecting sets of fluted surfaces oneupon the other and upon the inside surface of the lens. This makes iteasy to keep the exterior surface of the lens clean and it makes itpossible to mold such a lens by the utilization of a single mold partprovided with fluted surfaces.

In constructing lenses with the fluted surfaces thereof intersecting oneanother and disposed on either one or both .sides of the surface of thelens, it has been the custom to design the lens in such a Way as toprovide the intersecting flutes of each of the parallel sets of fluteswith constant radii of curvature from one end to another of the axis ofcurvature of each flute. With such a lens the pattern of light projectedin front of the handlamp and upon a vertical screen may be made ofrectangular formation but when this light is projected beyond such avertical screen and upon a horizontal screen or the ground thisrectangular pattern will become a trapezoidal pattern or a pattern whichincreases in Width as the distance from the vehicle increases.

It is now proposed to change a lens of this general character in such away as to provide a trapezoidal pattern of light upon a vertical screenand a rectangular pattern of light upon a horizontal screen or theground.

An object of the invention therefore is the manufacture of a lensdesigned to project a light pattern in such a manner asto diffuse thelight throughout a greater angle adjacent the bottom of the lens than atthe top thereof. Another object of the invention is to provide a methodand apparatus for manufacturing a light diffusing lens having aplurality of intersecting and parallel fluted surfaces thereon, with theradii of curvature of parallel flutes extending horizontally withrespect to the lens being constant from one end to another of the axisof curvature of each flute and the radii of curvature of the parallelflutes extending vertically of the lens being variable from one end toanother of the axes of curvature of each of such vertical flutes.

For a better understanding of the invention reference may now be had tothe accompanying drawing in which:

Figure 1 is a rear elevational view of a headlamp with parts broken awayand in section and having a lens embracing the principles of theinvention.

Figure 2 is a diagrammatical illustration of the optics involved in theprojection of light from a light source through one of the lightdiflfusing elements of the lens illustrated by Figure 1.

Figure 3 is a perspective view of a section of a mold for making lensesembracing the principles of the invention and of a tool employed in theconstruction of such a mold section. Figure 3 illustrates a mold sectionfor forming the inside surface of a flat or planular lens, asdistinguished from a curved lens, such as sometimes are employed inheadlamps for tractors and other automotive vehicles.

Figure 4 is a cross-sectional view of a mold section similar to thatillustrated by Figure 3, except that the mold section illustrated inFigure 4 is of arcuate cross section, such as is required in makingcurved lenses for tractors and other automotive vehicles. Figure 4 showsthe tool for constructing the mold as the tool is employed in formingthe contiguous and compound fluted surfaces of the mold.

In Figure l of the drawing there is employed for the purpose ofillustration a headlamp 10 comprising a reflector casing 11 and a lens12, the lens 12 being adapted to diffuse the light from the light sourceor bulb positioned within the reflector casing 11 and behind the centralportion of the lens 12. The light source or bulb is positioned withrespect to the light reflector in casing 11 in such a manner as toproject forwardly and against the inner surface of the lens 12 aninfinite number of relatively parallel rays of light such as areindicated at 13 in Figure 2.

The lens 12 comprises a plurality of contiguous lens sections indicatedat 14, each of the sections 14 comprising a compound surface generatedby radii of curvature extending from ditferent and angularly relatedaxes of curvature of the surface.

The lens sections 14 are arranged in contiguous relation to one anotherupon the inner surface of the lens 12 in horizontally and verticallydisposed rows of sections, or flutes, which are indicated generally at16 and 17, respectively. These rows of sections or flutes are formed byparallel flutes 16 extending horizontally of the lens 12 and parallelflutes 17 interposed upon the horizontal flutes 16 and extendingvertically of the lens 12.

A perspective View of one of the lens sections 14 is indicated in Figure2 and in this lens section the curve line or element 18 indicates theradius of curvature of the horizontal fluted sections indicated by thenumeral 16 in Figure 1. The radius of curvature is constant from one endto another of the fluted surfaces 16, this being the same as the radiusof curvature of the line or element 18 indicated by Figure 2.

The radii of curvature of the vertical flutes 17 are variable fromtop tobottom of each of the flutes. For example, lines 19 and 21 in Figure 2indicate elements of curvature of the surface of flutes 17 that differin radius of curvature. that the radius of curvature of the line. orelement 19 is greater than the radius of curvature of the element orline 21, and that the radii of curvature of the compound It will beapparent from Figure 2.

3 surface indicated at 22 increase constantly and progressively withrespect to the axis of curvature of the curve elements 19 and 21 andwith respect to the curvature of line of curve element 181 Also it willbe apparent from examining Figures 1 and 2 that the lines or elements 19and 21 lie approximately in the planes of the opposite edges of each ofthe fluted surfaces 16 so that each of the vertically fluted surfacesconsists of a plurality of horizontally curved elements of decreasingradii of curvature from one edge to another of the fluted surfaces 16.

As will be apparent from examining Figure 2, one of the parallel rays 13striking the upper adjacent corner of the lens section 14 will berefracted inwardly with respect to the curvature of the element ofcurvature 19 and upwardly with respect to the curvature of the elementof curvature 13, as'is indicated at 25, and, at the focal point 24 willcrossan'o ther ray of light indicated at 26 which is refracted inwardlyand upwardly, respectively, with respect to the upper remote corner ofthe elements 19 and 18 of the lens section14. Likewise parallel rays oflight indicated by the numeral 13 will impinge upon the surface 22 ofthe lens section 14' at the extremities of the curve element 21 and willrefract inwardly and downwardly as is indicated at'27 and 28 and willintersect at focal point 29. Since the radius of curvature of the lineor element 21 is less than the radius of curvature of the line orelement 19, the rays of light indicated by the lines 27 and 28 willconverge to a greater extent on passing through the lens section 14 thanwill the rays of light indicated at 23 and 26. The focal point 29therefore will be nearer the lens section 14 than will the focal point24. I I

Ifavertical screen, indicated at 31, is disposed in front of the lenssection 14, the rays of light 23, 26, 27, and 28 will define the cornersof a trapezoidal pattern of light incident upon the screen 31 as isindicated at 32.

It will also be apparent from Figure 2 that rays 23, 26, 27, and 28 whenprojected upon a horizontal screen or'upon the ground will define'thecorner extremities of the rectangular pattern of illuminationindicatedat 33.

Since the lens section 14 is simply one of a plurality of vertical andhorizontal rows of lens sections comprising the lens unit 12, it will beapparent that these lens sections 14 each will impose upon a verticalscreen such as that indicated at 31, a trapezoidal pattern of lightwhich is also similar to that indicated at 32. Also it will be apparentthat all of the lens sections 14 will impose upon the ground a compositerectangular pattern of light similar to that indicated at 33. The lightpatterns from each of the sections 14 may be made to overlap one anotherto a greater or lesser extent depending upon the general curvatureof'the inner and outer surfaces of the lens 12, but the total pattern oflight developed by such overlapping patterns will not differ from thepattern of light made by each lens section 14, as is indicated at 32 ona vertical screen and at 33 on a horizontal screen or the ground.

In order to be able to construct a mold to make a lens such as thatindicated at 12 there is provided a tool indicated at 34 having an endmill type cutter 36 the surface of revolution of which is conoidalformed thereon. The cutter 36 is constructed in such way as to cut onecompound'surface complementary to the compound surface 22 of the lenssection 14 at a single operation of the cutting tool, and upon thesurface of either of the mold blanks or sections indicated at 37 and 40,in Figures 3 and 4. The mill or cutter 36 may have a plurality oflongitudinally disposed cutting teeth 38 formed about the axis thereofandthese will be'rotated by operation of the tool-34 in such a way as toemploy the cutting edges 39 of eachof the teeth 38 oi-removing metalfrom the blanks. The curvature of the cutting'edge 39 of each of thecutting teeth 38 corresponds tothe curvature of the horizontally flutedsurfaces 16 as is indicated at 18. The curvature of the verticallyfluted surfaces 17 will be formed by successive and similar applicationsof the tool 34 to the blanks 37 and 40, as is indicated in Figure 4 at41, 42, and 43. The application of the tool may be continued across themold sections until mold surfaces long enough to form the verticalflutes of the lens 12 have been provided. Each flute 17 of the lens isformed in a similar manner by successively and similarly applying thetool 34 to the surface of the blanks 37 or 40 across the widths of eachof the horizontal flutes.

It will be observed that the mill or cutter part 36 of the tool 34 isformed in such a way that the radii of the cutting edges 39 of the teeth38 are greater at the shank" end of the mill'than at the opposite orleading end'the'reof and, that this difference in radii ofcurvature'continues between the opp'ositeends of thecutter in such a wayas to follow the curvature of the cutting edges 39 which is also thecurvature of the horiz ontal flutes 16. The small end of the mill'or'cutter thereforejwill' cutjthe end part of each of the contiguouscompoundlsurfaces" of the mold that correspondstothecurvature'ofthefengi of the part or section 14'which is indicatedbythefct'tf've'aglj line 21. The opposite or larger end ofthef'cuttergfi accordingly cuts'the parts of suchsurfaces which'cori'eispond to the curvature of the end 'partjindicated at: 19.

After the molds 37 or 40 have'beenjformed in the manner previouslydescribed, theflle'ns 12"n'1ay be'made by molding the inner surface ofthe lensby contact with the mold parts 37 or 40, the opposite 'or'outer'sur'fact'aqf, the lens being made if desired by moldssimilarto'those indicated at 37 and 40 and complementary thereto butformed by continuous and'uninterrupted surfaces.

It will be apparent that when the lens 12 is formed by the use of moldssuch as those indicatedat37 angl 40, the lens will consist of aplurality of contiguous sections 14 each having compound surfaces suchas that indicated at 22 and that each of these'surfa'ces 22 forms'a'curved surface on the lens 12 which is complementary to theconfiguration of each section of the molds 37 or 40.

It will be apparent that the curvature 39at the edges of the cuttingteeth 38 of the cutting tool 36 maybe of any desired curvature. Forexample, in the drawingpthe' cutting edges are shown as having a convexcurvature, but these edges may even be straight line edges or may beconvexly curved edges, depending upon the beam pat-l tern desired. Aconvex flute having the same radius'as' that shown would have the samelight distribution; Ordinarily the radius of curvature usedwill bedictated by the vertical spread desired at the base of the beam; Also,occasion might arise when it might be desirabletd make a beam patternwith the tapering sides of the trapezoid curved inwardly or outwardly,and it'mighfbe desirable to bunch the light rays at the top of the' beamto provide a hot spot or bright band at this portion of the pattern. Forconstructing such patterns, the cutter; and lens curvature will be adeveloped curve of any suit; able pattern rather than a curve with auniform radius and the same center of curvature.

We claim:

1. In amethod for shaping a lens mold, the 'stepfof forming arectangular surface of curvature 'in amold blank by engaging the surfaceof said mold blank with a rotating shaping tool, the mold engaging,portionjpf which develops a conoidal surface during rotation thereofabout its axis to thereby form a conoidal recessin said surface, saidaxis being disposed at an acute angleto the: surface engaged such thatside edges of the said conoidal recess are substantially parallel.

2. In a method for shaping a lensmold, thefstep'of forming a rectangularsurface of curvature in'amold blank by engaging the surface of said moldblank with' a rotating shaping tool, the mold engaging portions of whichare concavely curved cutting edges which develop a conoidal surfaceduring rotation of said toolaboutfits' axis to thereby form a conoidalrecess 'in said surface, said axis being disposed at an acute angleto'th'eiurfa'ce engaged such that side edges of the said conoidal recessare substantially parallel.

References Cited in the file of this patent UNITED STATES PATENTS LathamJuly 28, 1914 Loomis July 10, 1923 Coffey Dec. 4, 1923 Savidge June 17,1930 6 Hucal June 4, 1935 Falge Nov. 15, 1938 Pond May 8, 1951 SchenkApr. 7, 1953 OTHER REFERENCES Rowe: Engineering Descriptive Geometry,N.Y., D. Van Nostrand Co., Inc., 1939, p. 147 f.

